Cooled airfoil

ABSTRACT

A hollow air-cooled turbine blade has a web extending from face to face of the blade to divide the interior of the blade into two spanwise-extending chambers. A thin sheet metal liner is disposed in each chamber, the liner having perforations distributed over its surface and having projections to space it from the blade wall. The liner is flexible and may be folded substantially flat for insertion into the end of the blade. At the leading edge of the blade, the liner walls are recurved to define a generally parallel-walled slot nozzle extending spanwise of the blade. Additional holes are placed along the outlet from this nozzle to flow additional air for entrainment by the jet emerging from the slot nozzle to improve cooling of the leading edge. Cooled air enters the liners through the blade stalk and is discharged preferably through the tip and trailing edge of the blade.

United States Patent [191 Aspinwall a Apr. 23, 1974 COOLEI) AIRFOIL [75]Inventor: Robert H. Aspinwall, Zionsville, Ind.

[73] Assignee: General Motors Corporation,-

' Detroit, Mich.

[22] Filed: Aug. 30, 1972 [21] App]. No.: 284,715

5 l Field of Search......416/92, 96, 97, 95, 415/] [56] References CitedUNITED STATES PATENTS 3,032,314 5/1962 David 416/96 3,635,587 1/1972Giesman et al. 416/97 FOREIGN PATENTS OR APPLICATIONS 491,903 4/1953Canada 416/96 1,222,565 2/1971 Great Britain fll6/97 PrimaryExaminerEver ette A. Powell, Jr. Attorney, Agent, or Firm-PaulFitzpatrick [57] ABSTRACT A hollow air-cooled turbine blade has a webextending from face to face of the blade to divide the interior of theblade into two spanwise-exte'nding chambers. A thin sheet metal liner isdisposed in each chamber, the liner having perforations distributed overits surface and having projections to space it from the blade wall. Theliner is flexible and may be folded substantially fiat for insertioninto the end of the blade. At the leading edge of the blade, the linerwalls are recurved to define a generally parallel-walled slot nozzleextending spanwise of the blade. Additional holes are placed along theoutlet from this nozzle to flow additional air for entrainment by thejet emerging from the slot nozzle to improve cooling of the leadingedge. Cooled air enters the liners through the blade stalk and isdischarged preferably through the tip and trailing edge of the blade. i

5 Claims, 6 Drawing Figures PMENTEMR 23 m4 (1806; 275

sum 2 OF 2 IZO- WITH TURBULENCE PROMOTER LI. LU 8 8O CC A LL] u. 0 NOTURBULENCE g PROMOTER 1,- LU I l NOZZLE TO PLATE SPACING COOLED AIRFOILDESCRIPTION My invention is directed to improved cooled turbine bladesand the like. My invention is particularly directed to improvedstructures employing the principles of convection and impingementcooling. As used here,

the term convection cooling refers to the transfer of heat from theinterior of a blade wall to a cooling medium flowing along the wall.Impingement cooling is a variation of convection cooling in which thecooling medium is directed as a sheet or jet toward the wall to becooled, thereby improving the efficiency of the heat transfer orprovidingfor increased heat transfer in particular localities such, forexample, as the leading edge 7 of a blade. The invention is particularlyconcerned with improvements of the cooling of the blade leading edge andwith improved structure of a blade liner for this purpose. It is alsoconcerned with a blade liner which may readily be installed in apreviously completed turbine blade such as a cast blade, for instance.

Convection cooling of a blade wall, as distinguished from impingementcooling, is described in Zimmerman U.S. Pat. No. 2,859,011,'Nov. 4,1958, and Emmerson et al, U.S. Pat. No. 3,446,480, May 27, 1969.Impingement cooling by air spouting from blade liners against the wallof a blade is described in Weise et al, U.S. Pat. No. 2,873,944, Feb.17, 1959. A blade including a liner with special provisions for jettingair to theleading edge of the blade for impingement cooling is disclosedin Giesman etal, U.S. Pat. No. 3,635,587, Jan. 18, 1972. i

The general object of my invention is to provide improved structure toaccomplish the sort of cooling described in these prior art patents andto provide a structure particularly suited to fabrication.

The nature of my invention and its advantages will be apparent to thoseskilled inthe art from the succeeding detailed description andaccompanying drawings of the preferred embodiment of the invention.

FIG. 1 is a fragmentary sectional view of a turbine wheel with ablade'mounted thereon.

FIG. 2 is an axonometrio view of a turbine blade.

FIG. 3 is a transverse sectional view of the, blade taken on the planeindicated by the line 3-3 in FIG. 1.

FIG. 4 is a greatly enlarged view of the leading edge portion of FIG. 3.

FIG. 5 is a fragmentary axonometric view of the blade liner.

FIG. 6 is a graph illustrating certain parameters of impingementcooling.

Referring first to FIGS. 1 and 2, there is illustrated a,

turbine wheel 2 having a rim 3 on which are mounted a ring offluid-reacting members or blading members 4, commonly known as blades.Each blade comprises a dovetail root 6, a stalk 7, a platform 8, and ablade proper or airfoil 10. The airfoil, as shown most clearly in FIG.3, is hollow and has a leading edge at 11 a trailing edge at 12, aconvex face 14, and a concave face lll spanwise of the blade through theplatform and to the tip of the blade which is partially closed by a tipclosure 20.

The stalk 7 is made up of two webs 22 diverging from the root to theplatform which define between them an air space 23 having openings atthe forward and rear faces of the stalk. The space within the stalkcommunicates'through the open inner end 24 of the blade with thechambers 18 and 19.

The blade root 6 is mounted in a suitably serrated slot in the wheel rim3. The blade is retained and flow of fluid between the wheel rim andplatforms is prevented by two cover plates or rings of cover plates 26and 27. These cover plates may be unitary or segmented. The details areimmaterial to the invention. Such plates are shown in U.S. Pat. No.3,446,480 referred to above, and in White U.S. Pat. No. 3,034,298, May15, 1962, for, example. Holes 28 in the plate 26 and 30 in the plate 27provide for entry of cooling air or other mefrom whichthe fluid flowsinto the blade stalk and thus into the passages 18 and 19. The: fluidultimately exhausts through openings 31 and 32 in the blade tip closureforward and rearward of the web 16, respectively. Also, preferably, thetrailing edge of the blade is formed with outlets such as slots 34 forexhaust of cooling air at this point.

The structure asso far described may be considered part of the knownstate of the art. To indicate generally the scale of the drawings, thespecific blade shown has a chord of about two inches.

To provide for air impingement and better flow of the cooling air alongthe interior of the surface of the blade wall, blade liners 35 and 36are provided extending spanwise of the blade in chambers 18 and 19,respectively. These liners are open at the platform end of the blade andclosed at the tip of the blade, and are made of very thin flexible heatresisting sheet metal, preferably about three to five thousandths inchthick. The liners are preferably spaced about twenty-five thousandthsinch from the blade wall, the spacing being accomplished by embossedprojections 38 extending outwardly from the liner. The liners have foldsas indicated at139 in the liner 35 and correspondingly in the liner 36.With these folds, the liner may be flattened or collapsed as indicatedgenerally by the broken line 40 so that the flattened liner may beinserted into the air space 23 in the blade stalk and'pushed on into thechamber 18 or 19. The liners may be made of such thin flexible materialbecause they are not a structural element of the blade and are containedor supported by the wallsof the blade and the internal air pressure.After insertion, the liner may be expanded into contact with the bladewall by forcing a blast of fluid into the liner. Each liner has numeroussmall perforations distributed over its surface as indicated generallyat 41 in FIGS. 2, 4, and 5. Air which flows from the'liner through theseholes impinges against the inner surface of the blade wall and flowsbetween the blade wall and liner to the outlets at 31, 32, and 34. Theseperforations may be about seven thousandths inch in diameter.

Considering now the structure of the liner 35 at the leading edge of theblade (FIGS. 4 and 5), the two sides or faces of the liner are recurvedto define the side walls 42 of a slot nozzle 43. As shown most clearlyin FIG. 5, these side walls are united by spacers 44 which are stripsextending between the two walls 42 and brazed, welded, or otherwisefixed to them. The slot nozzle atits discharge'end thus terminates ingenerally cylindrical outwardly flaring wall sections 46. A row of holes47 extends through each of these wall sections 46 in position to delivercooling air into the sheet of air issuing from the slot nozzle 43.

The distance from slot 43 to the interior of the leading edge of theblade may be about fifty thousandths of an inch and the width of theslot preferably at least as great as one-eighth that distance,preferably about seven thousandths. The jet issuing from the slot nozzlehas a greater penetrating power than that issuing from a simple holesuch as 41 through the sheet metal. However, the distance from the holes4l'to the blade wall is less.

With the flat jet issuing from the nozzle 43, this moving sheet of airtends to draw air from the holes 47 in the flaring part of the slotnozzle,'which air mixes with the flow from the slot nozzle and creates agreater mass flow, greater momentum, and greater turbulence at the pointof impingement for greater removal of heat from the blade leadingedge.

FIG. 6 shows curves of heat transfer coefficient as a function of theratio of nozzle to plate spacing to nozzle width, the upper curveindicating conditions with the turbulence promoter (additional airthrough 47). It will be noted that the heat transfer coefficient issignificantly higher with the turbulence promoter, particularly asnozzle to plate spacing decreases below eight times the width of thenozzle.

The impingement tubes 35 and 36 may be fixed to the nozzle by welding,diffusion bonding, or a brazing operation at the area of the platform 8.Preferably, the margins of the liner are spread to lie under theplatform and are electron beam welded to the platform at that point.Alternatively, the liners may be welded to the interior of the blade atits base. While it is considered less feasible, it should be noted thatthe spacing of the liner from the blade may be accomplished byprotrusions from the inside of the blade rather than from theprojections 38 on the liner.

As a matter of fabrication, it is also possible to diffusion bond theliner to the interior of the blade or airfoil and thereafter fix theblade'to the base or other mounting structure. In the case ofa turbinenozzle, which may be regarded as. a special case in which the blades arestationary, the attachment of the blade to the shrouds or otherstructure defining the flow path through the turbine may follow knownpractice. In this case, since there is no centrifugal force on the vane,retention of the liner is easier. If the liner is open at both ends, andthe vane is supplied with air from both ends, there is not even any gaspressure tending to displace the liner.

prising, in combination, a hollow blade having leading and trailingedges and defining a spanwise-extending chamber, and a perforated bladeliner disposed in the chamber, the end of the blade defining an openingfor insertion of the liner, the liner conforming generally to thecontour of the interior of the blade and being spaced from the bladewall, the liner including means defininga spanwise-extending slot nozzlefor discharge of a cooling fluid directed at the leading edge of theblade and generally cylindrical diverging walls at the outlet of thenozzle, and defining perforations through the said diverging walls forflow of additional cooling fluid for entrainment by the flow through theslot nozzle.

2. An internally cooled turbine blading element comprising, incombination, a hollow blade having leading and trailing edges and a webdisposed intermediate the said edges, so that the blade defines twospanwiseextending chambers, one at each side of the web, and aperforated blade liner disposed in each chamber, the end of the bladedefining openings for insertion of the liners, each liner conforminggenerally to the contour of the interior of the blade and being spacedfrom the blade wall, the liner at the leading edge of the bladeincluding means defining a spanwise-extending slot nozzle for dischargeof a cooling fluid directed at the leading edge of the blade andgenerally cylindrical diverging walls at the outlet of the nozzle, anddefining perforations through the said diverging walls for flow ofadditional cooling fluid for entrainment by the flow through the slotnozzle.

3. An internally cooled fluid-reacting member for a turbomachinecomprising, in combination, wall means defining a blade with a centralchamber having an opening at one end of the blade, a tubular perforatedliner of thin flexible sheet metal disposed in the chamber, and spacermeans maintaining a separation between the liner and the wall means overthe major portion of the area of the liner, the liner being collapsiblefor insertion into the chamber through the said opening and beingexpandable by air pressure after such insertion to the extent allowed bythe spacer means, the liner including means at the leading edge of theblade defining a spanwise-extending slot nozzle for a discharge of acooling fluid directed at the leading edge of the blade and generallycylindrical diverging walls at the outlet of the nozzle, and definingperforations through the said diverging walls for flow of additionalcooling fluid for entrainment by the flow through the slot nozzle. i I

4. An internally'cooled turbine blading element comprising, incombination, a root, a stalk, and a hollow blade extending from thestalk, the blade having leading and trailing edges and defining aspanwiseextending chamber, and a perforated blade liner disposed in thechamber, the stalk and the stalk end of the blade defining openings forinsertion of the liner, the liner conforming generally to the contour ofthe interior of the blade and being spaced from the blade wall, theliner including means defining a spanwiseextending slot nozzle fordischarge of a cooling fluid directed at the leading edge of the bladeand generally cylindrical diverging walls at the outlet of the nozzle,and defining perforations through the said diverging walls for flow ofadditional cooling fluid for entrainment by the flow through the slotnozzle.

5. An internally cooled turbine blading element comprising, incombination, a root, a stalk, and a hollow blade extending from thestalk, the blade having leading and trailing edges and a web disposedintermediate the said edges, so that the blade defines twospanwiseextending chambers, one at each side of the web, and

6 rected at the leading edge of the blade and generally cylindricaldiverging walls at the outlet of the nozzle, and defining perforationsthrough the said diverging walls for flow of additional cooling fluidfor entrainment by the flow through the slot nozzle.

1. An internally cooled turbine blading element comprising, incombination, a hollow blade having leading and trailing edges anddefining a spanwise-extending chamber, and a perforated blade linerdisposed in the chamber, the end of the blade defining an opening forinsertion of the liner, the liner conforming generally to the contour ofthe interior of the blade and being spaced from the blade wall, theliner including means defining a spanwise-extending slot nozzle fordischarge of a cooling fluid directed at the leading edge of the bladeand generally cylindrical diverging walls at the outlet of the nozzle,and defining perforations through the said diverging walls for flow ofAdditional cooling fluid for entrainment by the flow through the slotnozzle.
 2. An internally cooled turbine blading element comprising, incombination, a hollow blade having leading and trailing edges and a webdisposed intermediate the said edges, so that the blade defines twospanwise-extending chambers, one at each side of the web, and aperforated blade liner disposed in each chamber, the end of the bladedefining openings for insertion of the liners, each liner conforminggenerally to the contour of the interior of the blade and being spacedfrom the blade wall, the liner at the leading edge of the bladeincluding means defining a spanwise-extending slot nozzle for dischargeof a cooling fluid directed at the leading edge of the blade andgenerally cylindrical diverging walls at the outlet of the nozzle, anddefining perforations through the said diverging walls for flow ofadditional cooling fluid for entrainment by the flow through the slotnozzle.
 3. An internally cooled fluid-reacting member for a turbomachinecomprising, in combination, wall means defining a blade with a centralchamber having an opening at one end of the blade, a tubular perforatedliner of thin flexible sheet metal disposed in the chamber, and spacermeans maintaining a separation between the liner and the wall means overthe major portion of the area of the liner, the liner being collapsiblefor insertion into the chamber through the said opening and beingexpandable by air pressure after such insertion to the extent allowed bythe spacer means, the liner including means at the leading edge of theblade defining a spanwise-extending slot nozzle for a discharge of acooling fluid directed at the leading edge of the blade and generallycylindrical diverging walls at the outlet of the nozzle, and definingperforations through the said diverging walls for flow of additionalcooling fluid for entrainment by the flow through the slot nozzle.
 4. Aninternally cooled turbine blading element comprising, in combination, aroot, a stalk, and a hollow blade extending from the stalk, the bladehaving leading and trailing edges and defining a spanwise-extendingchamber, and a perforated blade liner disposed in the chamber, the stalkand the stalk end of the blade defining openings for insertion of theliner, the liner conforming generally to the contour of the interior ofthe blade and being spaced from the blade wall, the liner includingmeans defining a spanwise-extending slot nozzle for discharge of acooling fluid directed at the leading edge of the blade and generallycylindrical diverging walls at the outlet of the nozzle, and definingperforations through the said diverging walls for flow of additionalcooling fluid for entrainment by the flow through the slot nozzle.
 5. Aninternally cooled turbine blading element comprising, in combination, aroot, a stalk, and a hollow blade extending from the stalk, the bladehaving leading and trailing edges and a web disposed intermediate thesaid edges, so that the blade defines two spanwise-extending chambers,one at each side of the web, and a perforated blade liner disposed ineach chamber, the stalk and the stalk end of the blade defining openingsfor insertion of the liners, each liner conforming generally to thecontour of the interior of the blade and being spaced from the bladewall, the liner at the leading edge of the blade including meansdefining a spanwise-extending slot nozzle for discharge of a coolingfluid directed at the leading edge of the blade and generallycylindrical diverging walls at the outlet of the nozzle, and definingperforations through the said diverging walls for flow of additionalcooling fluid for entrainment by the flow through the slot nozzle.